It is well known in the art that metals and metal compounds, preferably heavy metals and compounds thereof, are suitable catalysts for forming oxirane compounds by reaction of olefins with organic hydroperoxides. This is illustrated by U.S. Pat. Nos. 3,351,635; 3,468,099; and 3,375,362. It is also known to remove the catalyst from the reaction product or epoxidation effluent by contacting the effluent with a sufficient quantity of an aqueous basic solution to remove therefrom catalyst in combination with acidic reaction products. This is described in U.S. Pat. No. 3,523,956. In this procedure, there is produced an aqueous waste stream containing salts of the catalyst in admixture with salts of the organic acidic materials.
The procedure described in U.S. Pat. No. 3,523,956 provides a simple method for removing catalyst as well as acidic reaction products from the epoxidation effluent. There is, however, a major drawback with this procedure, as an aqueous waste stream of very large volume is produced containing the metallic catalyst as well as the neutralized acids and phenols. For environmental reasons it is out of the question to discharge this waste stream directly into public waters such as a stream, river, bay or the like. Consequently, some type of waste treatment procedure is required. Further, the problem of waste treatment is technically very complex because of the large waste volume and the conjoint presence of the catalyst and the neutralized acidic materials.
Removal of the organic constituents from aqueous saline wastes is conventionally accomplished by either of two means, incineration or biological degradation. However, attempts to use either method with the waste from the prior process are greatly hindered by the presence of the metallic catalyst. On the one hand, incineration has been found to be unworkable because the incineration equipment becomes fouled with accumulations of solid deposits containing the catalyst, and also because air pollution problems arise through volatilization of some catalyst into the flue gas. Further, the metallic catalyst fouls heat transfer surfaces and makes it impossible to recover useful energy from the incinerator, for example, by generating steam. On the other hand, disposal by biological degradation is also unsatisfactory because of toxic effects of the catalyst on the bacteria population. Thus, elimination of the organic constituents is extremely difficult.
Moreover, even if the organic constituents could somehow be eliminated, there would remain the problem of removing the metallic catalyst, since discharges of heavy metal substances of this type are environmentally restricted. Such removal is impeded by the large volume of water which must be treated to remove small quantities of catalyst, generally much less than one percent.
In addition to the abovementioned environmental disadvantages, the prior process is not amenable to recovery and recycle of potentially valuable chemicals as well as fuel values in the waste stream. The presence of the catalyst strongly hinders attempts to recover and re-use the basic material in the aqueous solution. Additionally, the presence of large quantities of salts of the basic material and the organic acidic materials makes it extremely difficult to recover and re-use the catalyst in the epoxidation process.
The present invention eliminates these difficulties. It has been discovered that by utilizing a two stage procedure, substantially all of the metallic catalyst can be selectively removed in a first stage, and acidic materials neutralized in a second stage. This procedure is surprisingly selective in that one can obtain a relatively small volume of material containing essentially all of the catalyst, in order to have a modest amount of material which can be treated for recovery of the catalyst or disposal of the same.
Therefore, rather than having an environmental problem with a relatively large volume of solution containing all of the metallic catalyst and a large proportion of the acidic/phenolic materials, as obtained in the prior process, the process of this application enables one to produce a relatively small volume of solution containing substantially all of the metallic catalyst but only a small proportion of the acidic/phenolic materials.
Then from the second stage a relatively large volume of material containing the neutralized acids and phenols, with only a small, innocuous catalyst content, can be disposed readily by conventional means, for example, by incineration or biological treatment A particularly preferred option, with major chemical and energy savings, is to treat these neutralized acids and phenols in a fluidized bed incinerator and thereby recover valuable sodium carbonate and sodium bicarbonate.
The two step process of the present invention is therefore much more advantageous than the prior process, on an environmental basis and based on energy savings and recovery of valuable chemicals, despite its greater complexity.